Effective quad-detector occupancy sensors and motion detectors

ABSTRACT

A method and apparatus for improving the sensitivity, angular resolution and range of motion detectors, occupancy sensors and similar systems are described. Specifically, an improved infrared input and detection section is described which utilizes two dual-detectors configured to optimally operate equivalent to a single quad-detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Application Serial No. 60/231,595 filed on Sep. 11, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to passive infrared motion detectors,occupancy sensors and similar devices, and more particularly to theinfrared input section and detection system of these devices.

2. Description of the Related Art

Passive infrared motion detectors and occupancy sensors employ an arrayof Fresnel lenses covering an entrance aperture. This lens array isilluminated by thermal infrared radiation from the object of interest.For any particular angle of incidence each of the elements in the lensarray covering the entrance aperture generates a focal spot. The arrayof lenses is designed so that as the object of interest moves across itsfield of view the system of focal spots moves across the sensitive areaof a detector. The varying electrical output signal generated by thedetector is processed to yield information about the state of motion ofthe object of interest.

Each element of the lens array is designed to focus incident infraredradiation in a small angular range onto the sensitive area of adetector. The (active) angular sectors in which the elements of the lensarray focus incident infrared radiation onto the sensitive area of adetector are interlaced by (passive) angular sectors within whichincident infrared radiation is not focused onto the sensitive area ofthe detector by any element of the lens array. Moving infrared radiatorsare detected when they move from one angular sector across a boundaryinto an adjacent angular sector leading to a rapid change in the amountof infrared power falling on the sensitive area of the detector.Ordinarily, the sectors are all approximately the same angular size andthe maximum angle through which a radiating object of interest can movewithout being detected, i.e. the angular resolution of the system, isequal to the angular size of one of these sectors. This assumes that thesize and velocity of the radiating object and its distance from theentrance aperture are such that the intensity of the infrared signal isgreater than the minimum that can be detected by the system electronics.

One way to improve the angular resolution of the system is to increasethe number of elements in the lens array. More specifically, for anentrance aperture of fixed size the angular resolution of the system isapproximately inversely proportional to the number of elements in thelens array. Thus, in order to achieve the smallest angular resolution, alens array with as many elements as possible must be employed. On theother hand, the sensitivity and effective range of the system decreaseif the size of the individual lens elements of the array is decreased.The phrase “sensitivity of the system” refers to the size of thesmallest radiating object that can be detected as a function of itsdistance from the detector. Thus, compromises must be made between thesize of the entrance aperture, sensitivity, range and angular resolutionof the system. For example, for any desired sensitivity and range thereis a minimum size for each of the individual lenses of the array andhence a maximum number of elements for an entrance aperture of fixedsize and a corresponding minimum angular resolution.

SUMMARY OF THE INVENTION

The present invention is a new input lens configuration and detectionscheme which can be employed, for example, to: 1) increase thesensitivity and range of motion detectors and occupancy sensors with anentrance aperture of fixed size without decreasing the angularresolution of the system or, 2) improve the angular resolution of asystem with an entrance aperture of fixed size without decreasing thesensitivity or range of the system or, 3) decrease the size of theentrance aperture required for a given sensitivity, range and angularresolution or, 4) reduce the distance that the unit must protrude in,for example, a wallbox installation in order to achieve acceptableperformance at wide angles. The relative importance of each of thesecharacteristics of motion detectors and occupancy sensors depends on theapplication in which the system is employed.

In simplest terms, the infrared input section and detection schemedisclosed herein consists of an array of lens elements followed by afirst radiation detector including a pair of sensitive areas and asecond radiation detector having a pair of sensitive areas. The pair ofdual detectors, such as, for example pyrodetectors are positioned sothat as the direction of incident radiation varies, at least one elementof the lens array at least partially focuses the incident radiation ontoat least three of the four sensitive areas of the two detectors, therebyforming an effective quad-detector. Typical pyrodetectors used in priorart occupancy sensors and motion detectors have two sensitive areas ontheir surface each of which is 1 mm wide, separated by 1 mm. As a focalspot of any particular element of the lens array moves across this 3 mmregion, four electrical signals are generated as the spot moves onto oroff of a sensitive area. These signals are generated as the infraredsource moves across the angular boundaries which separate regions ofspace where the focal spot is on a sensitive area as opposed to regionsof space where the focal spot is not on one of the sensitive areas ofthe detector. Motion detectors and occupancy sensors which employ adetector with two sensitive areas can achieve improved performance ascompared to units that employ a detector with only one sensitive area,since each focal spot gives rise to four electrical signals as theinfrared source moves as opposed to two electrical signals for adetector with only one sensitive area. In many applications a detectorsystem with three or four sensitive areas can improve the performance ofthe occupancy sensor/motion detector beyond that achievable with adetector with only two sensitive areas.

The difficulty with using two detectors side, by side in order to obtainfour sensitive areas, is that because of the physical size of apyrodetector the sensitive areas on one detector are much more than 1 mmfrom the sensitive areas on the other detector. Because of this, theangular regions which define those regions of space wherein a focal spotis on an sensitive area as opposed to those angular regions where afocal spot is not on a sensitive area are not even approximatelyuniformly distributed. Nevertheless the infrared input section anddetection scheme disclosed herein is capable of producing an almostuniform distribution of these angular sectors. For the purpose ofillustration, suppose that a certain range, angular resolution andsensitivity can be achieved by employing some particular lens array. Ifthe number of elements of the array and their size is not changed, but aquad-detector of the type disclosed herein is employed, the number ofelectrical signals is effectively doubled as an infrared source movesacross the field of view of the lens array. The angular resolution hasbeen improved by a factor of two. Alternatively, if a quad-detector ofthe type disclosed herein is employed and the number of elements in thelens array is halved, the angular resolution is unchanged but theinfrared power in the focal spot is doubled with a correspondingincrease in range and sensitivity. In some applications the optimumdesign is a hybrid system which employs a traditional array of Fresnellenses and/or mirrors to cover some angular ranges and a design of thetype disclosed herein for other angular ranges.

Also, by employing a quad-detector of the type disclosed herein it ispossible to achieve the same performance with a much smaller entranceaperture. This is of importance, for example, in applications whereaccidental damage or casual vandalism of the entrance aperturelens/cover is a problem. One aesthetically appealing configuration is arocker switch (e.g. Leviton's Decora rocker switch) with a smallinfrared entrance aperture in the center, both vertically andhorizontally, of the rocker. This would convert the traditional rockerswitch to an “automatic switch” i.e. an ordinary switch with anoccupancy sensor feature. This aesthetically appealing configuration canalso be achieved without a quad-detector. However, a quad-detector canbe employed to enlarge the field of view and/or decrease the requiredaperture size for a given sensitivity and range. This technique can beapplied to other wiring devices e.g. toggle switches, dimmers, timers,outlets, etc. These new designs maintain the traditional appearance ofthe device while adding the occupancy sensor/motion detector feature inan inconspicuous way. As previously noted in each of these applicationsa quad-detector of the type disclosed herein may or may not be employeddepending on the specified size of the entrance aperture and therequired field of view, sensitivity and range.

For any occupancy sensor or motion detector, the field of view can beincreased by employing mirrors adjacent to the entrance aperture toreflect wide angle rays towards the center of the system. These mirrorsmay be positioned before or after the lens array. Further, in someapplications the optimum system is a hybrid in which the mirrors directand/or focus infrared radiation from some angular sectors directly ontoa detector while infrared radiation in other angular sectors is passedthrough the lens array to the detector. Infrared radiation from otherangular sectors may be processed differently.

All of the preceding is equally applicable to, for example, wall andceiling units, indoor and outdoor units in lighting, heating,ventilation and/or security applications. Also, it is equally applicableto passive and active infrared and optical systems. Further, theimplementations disclosed herein may be used in single technologysystems or in combination with motion detectors/occupancy sensors basedon other technologies e.g. active infrared, ultrasonic or microwavesystems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent in light of the following detaileddescription of the preferred embodiments thereof taken in conjunctionwith the attached drawings in which:

FIGS. 1A-D are schematic diagrams illustrating an exemplary embodimentof the infrared input section and detection scheme of motion detectorsand occupancy sensors employing an infrared input section and detectionscheme in accordance with the present invention;

FIGS. 2A and 2B are a schematic diagrams illustrating the angularsectors which define the angular resolution of an exemplary embodimentof motion detectors and occupancy sensors employing an infrared inputsection and detection scheme in accordance with the present invention;

FIG. 3 is a schematic diagram illustrating an exemplary embodiment ofthe infrared input section of motion detectors and occupancy sensorsemploying an infrared input section and detection scheme and wide anglemirrors in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, in which like reference numerals identifysimilar or identical elements throughout the several views, FIG. 1illustrates the infrared input and detector sections of one possibleembodiment of a passive infrared motion detector or occupancy sensorwhich employs an array of lens elements and a quad-detector system ofthe type disclosed herein.

With reference to FIG. 1A, a Fresnel lens array 11 spans the entranceaperture of a motion detector housing 10. Each element of the lens array11 intercepts a small fraction of the input infrared radiation 12incident from some particular direction and focuses it to a spot in thefocal plane of that element, e.g. 13 is the focal point of the firstelement of the lens array to the right of the vertical centerline 14.Accordingly, the number of focal spots is equal to the number ofelements of the lens array 11. As the source of the infrared radiation12 moves (such as, for example in the direction of arrow A in FIG. 2A),the angle of incidence of the incident infrared radiation 12 changes andthe system of focal spots moves across the four sensitive areas of thequad-detector 15 (such as, for example, in the direction of arrow B inFIG. 1A). This detector consists of two dual detectors positioned neareach other as illustrated.

As the infrared source moves, the electrical output of the detectorchanges abruptly as a focal spot moves onto or off of any one of theplurality of sensitive areas 16-19 of the quad-detector 15. As theincident direction of infrared radiation changes from nearlyperpendicular to the entrance aperture clockwise towards the directionof radiation indicated by 12, the focal spot 13, for example, moves fromthe extreme right hand side of the right most sensitive area of thequad-detector (see FIG. 1A) towards the left and eventually off of theleft hand side of the sensitive area 17(see FIG. 1B), typically adistance of 3 mm. Further clockwise rotation of the direction ofincidence moves the focal spot 13 from the left hand edge of sensitivearea 17 to the right hand edge of sensitive area 18 (see FIG. 1C). Aseparation of approximately 5 mm is preferred between the left hand edgeof sensitive area 17 and the right hand edge of sensitive area 18. Withthis detector geometry the angular separation between the two activeangular sectors generated as the focal spot crosses sensitive areas16-17 and the two active angular sectors generated as the focal spotcrosses sensitive areas 18-19 is precisely the correct size to containfive angular sectors (two active, three passive) generated by anotherelement of the lens array 11. This is discussed further in connectionwith FIG. 2 below.

It is fortuitous that dual pyrodetectors commonly employed in occupancysensors and motion detectors are manufactured in standard TO-39 or TO-5housings which have a diameter of 8.1 mm, for example, Heimann LHi874,LHi878 and LHi968. This is only 0.1 mm larger than the ideal of 8 mmrequired to obtain a 5 mm separation of the two innermost sensitiveareas of the detector. These housings have a thin rim at the bottom witha diameter of 9.2 mm. If two housings of this type are placed side byside the distance between the two innermost sensitive areas is 6.2 mmwhich is approximately 25% larger than the ideal separation of 5 mm. Inmost applications this is a tolerable departure from the ideal, somepairs of angular sectors would be 25% larger than adjacent pairs.Alternatively, the rim can be partially removed or the top surfaces ofthe two detectors can be tipped a few degrees towards each other. Thiswould be sufficient to reduce the distance between the two innermostsensitive areas to the ideal of 5 mm.

FIG. 2A illustrates the edges 21-24 of the angular regions defined bythe focal spot 13 crossing the four edges of the sensitive areas 16-17of the quad-detector (see FIGS. 1A and 1B). The edges 25-28 (see FIG.2B) correspond to the focal spot 13 crossing the four edges of thesensitive areas 18-19 of the quad-detector (see FIGS. 1C and 1D). Thesetwo groups of four edges are separated by an angular regioncorresponding to the separation between the left hand edge of sensitivearea 17 and right hand edge of sensitive area 18. Notice that if thisseparation is 5 mm as opposed to a 1 mm separation of sensitive areas of1 mm width, then the angular size of this region is precisely correct tocontain two active angular regions and three passive angular regions.These five angular sectors are generated by the focal spot 13 a of asecond element of the Fresnel lens array passing from the right handedge of sensitive area 16 (see FIG. 1B) to the left hand edge ofsensitive area 17 (see FIG. 1C). A second group of five sectorsclockwise from the group 25-28 is generated as this second focal spot(13 a) moves from the right hand edge of sensitive area 18 (see FIG. 1D)to the left hand edge of sensitive area 19. Thus by employing aquad-detector of the type disclosed herein two elements of the lensarray 11 produce twice as many edges as the same two elements wouldproduce with a prior art dual detector. This can be used to double, forexample, the number of angular sectors produced by a given number ofarray elements without reducing the range or sensitivity of the system.Alternatively, doubling the size of the elements of the lens arraydoubles the power received by any array element with a correspondingincrease in range and sensitivity without sacrificing angularresolution. This process can be repeated for each pair of array elementson each side of the vertical centerline 14 of the system. An unpairedelement if necessary, can be used to generate an additional pair ofactive sectors. Of course it is also possible to double the width of alens array element and halve its height. With the detection schemedisclosed herein this would leave the performance characteristics of thesystem unchanged but make room for another tier of Fresnel lenses whichcould be employed in a number of ways. Finally, it is not necessary totreat each element of the lens array in the same way or to restrict thechanges to doubling and halving which were only used for the purpose ofillustration.

FIG. 3 is a schematic diagram of the input lens and detection system ofthe present invention supplemented with wide angle mirrors 31. Thesemirrors perform the same function as previously described in U.S. Pat.No. 5,929,445, which is incorporated herein by reference, in connectionwith occupancy detectors and motion detectors employing prior artdetection schemes.

While the present invention has been described in detail with referenceto the preferred embodiments, they represent mere exemplaryapplications. Thus, it is to be clearly understood that many variationscan be made by anyone of ordinary skill in the art while staying withinthe scope and spirit of the present invention.

What is claimed is:
 1. A radiation detection system, comprising: ahousing including a surface having an opening for receiving incidentradiation; an array of lens elements disposed across said opening ofsaid housing; a first radiation detector including a pair of sensitiveareas; and a second radiation detector including a pair of sensitiveareas, wherein said first and second radiation detectors are positionedso that as the direction of the incident radiation varies, at least oneelement of the lens array at least partially focuses the incidentradiation successively onto at least three of four sensitive areas, eachof said sensitive areas generating an abrupt change in electrical outputto activate an alarm in response to focused incident radiation movingonto or off of any one of the at least three of four sensitive areas. 2.The radiation detection system according to claim 1, wherein said lensarray is a Fresnel lens array.
 3. The radiation detection systemaccording to claim 1, wherein said first detector is positioned adjacentto said second detector.
 4. The radiation detection system according toclaim 1, wherein each of said sensitive areas for each of said first andsecond detectors is about 1 mm wide and separated from one another byabout 1 mm.
 5. The radiation detection system according to claim 4,wherein said lens array has a center line and wherein said firstdetector is disposed on a first side of the center line and said seconddetector is disposed on a second side of the center line.
 6. Theradiation detection system according to claim 5, wherein said pair ofsensitive areas of said first detector are separated a distance of about5 mm from said pair of sensitive areas of said second detector.
 7. Theradiation detection system according to claim 5, wherein a sensitivearea of said pair of sensitive areas of said first detector is separatedby about 5 mm from a sensitive area of said pair of sensitive areas ofsaid second detector.
 8. The radiation detection system according toclaim 1, further comprising: means disposed within the housing adjacentto the opening and structured and arranged for directing radiationreceived thereon to the interior of the housing.
 9. The radiationdetection system according to claim 1, wherein said first detector incombination with said second detector define a quad-detector.
 10. Theradiation detection system according to claim 1, wherein said lens arrayfurther comprises: at least one additional element configured andadapted to at least partially focus incident radiation onto a sensitivearea of a detector for at least some angles of the incident radiationbetween those angles for which the at least one lens element at leastpartially focuses incident radiation onto a sensitive area of adetector.
 11. A radiation detection system, comprising: a housingincluding a surface having an opening for receiving incident radiation;an array of Fresnel lens elements disposed across said opening of saidhousing; and a radiation detector including at least four sensitiveareas positioned so that as the direction of the incident radiationvaries, at least one element of the lens array at least partiallyfocuses the incident radiation successively onto at least three of thefour sensitive areas each of said sensitive areas generating an abruptchange in electrical output to activate an alarm in response to focusedincident radiation moving onto or off of any one of the at least threeof four sensitive areas.
 12. The radiation detection system according toclaim 11, wherein the radiation detector comprises: a first sensitivearea; a second sensitive area spacially separated from said firstsensitive area; a third sensitive area spacially separated from saidsecond sensitive area on a side opposite said first sensitive area; anda fourth sensitive area spacially separated from said third sensitivearea on a side opposite said second sensitive area.
 13. The radiationdetection system according to claim 12, wherein said spacial separationbetween said first and second sensitive areas is about 1 mm.
 14. Theradiation detection system according to claim 12, wherein said spacialseparation between said second and third sensitive areas is about 5 mm.15. The radiation detection system according to claim 12, wherein saidspacial separation between said third and fourth sensitive areas isabout 1 mm.
 16. The radiation detection system according to claim 15,wherein said first, second, third and fourth sensitive areas arearranged symmetrically about a center line of the lens array.
 17. Theradiation detection system according to claim 15, wherein said pluralityof sensitive areas define a quad-detector.
 18. The radiation detectionsystem according to claim 12, wherein said spacial separation betweensaid first and second sensitive areas is about 1 mm, said spacialseparation between said second and third sensitive areas is about 5 mm,and said spacial separation between said third and fourth sensitiveareas is about 1 mm.
 19. The radiation detection system according toclaim 11, further comprising: directing means disposed within thehousing adjacent to the opening and structured and arranged to directradiation received thereon to the interior of the housing.
 20. Theradiation detection system according to claim 19, wherein said directingmeans includes at least one mirror disposed adjacent an edge of theopening.
 21. The radiation detection system according to claim 11,wherein said lens array further comprises: at least one additionalelement configured and adapted to at least partially focus incidentradiation onto a sensitive area of a detector for at least some anglesof the incident radiation between those angles for which the at leastone lens element at least partially focuses incident radiation onto asensitive area of a detector.
 22. A radiation detection system,comprising: a housing including a surface having an opening forreceiving incident radiation; an array of Fresnel lens elements disposedacross said opening of said housing, wherein said lens array includes acenter line; and a pair of dual detectors, wherein each of said pair ofdual detectors includes a pair of sensitive areas separated by about 1mm and wherein the pair of sensitive areas of a first of said pair ofdual detectors is separated from the pair of sensitive areas of a secondof said pair of dual detectors by about 5 mm, whereby said pair of dualdetectors defines a quad-detector, wherein the detectors are positionedso that as the direction of the incident radiation varies, at least oneelement of the lens array at least partially focuses the incidentradiation successively onto at least three of the four sensitive areaseach of said sensitive areas generating an abrupt change in electricaloutput to activate an alarm in response to focused incident radiationmoving onto or off of any one of the at least three of four sensitiveareas.
 23. The radiation detection system according to claim 22, whereinsaid lens array further comprises: at least one additional elementconfigured and adapted to at least partially focus incident radiationonto a sensitive area of a detector for at least some angles of theincident radiation between those angles for which the at least one lenselement at least partially focuses incident radiation onto a sensitivearea of a detector.
 24. A radiation detection system, comprising: ahousing including a surface having an opening for receiving incidentradiation; an array of lens elements disposed across said opening ofsaid housing; four independent, radiation-detecting sensitive areaspositioned so that as the direction of the incident radiation varies, atleast one element of the lens array at least partially focuses theincident radiation successively onto at least three of the foursensitive areas, each one of the four independent, radiation-detectingsensitive areas generating an abrupt change in electrical output toactivate an alarm in response to focused incident radiation moving ontoor off of any one of the four sensitive areas.